1. Field of the Invention
This invention relates to a filtering apparatus, and in particular to a blood filtering apparatus for separating and removing air bubbles and foreign substances from the blood being filtered.
2. Description of the Prior Art
In blood treatment systems in which blood removed from a patient is treated and then returned back to the patient, a filtering apparatus (blood filter) has been employed in the blood flow return line for separating and removing air bubbles and foreign substances from the blood.
These filtering apparatuses are generally referred to as blood filters or bubble traps. In this type of blood filter, a filtering material formed into a pleated shape has been employed to obtain a large filtering surface area, as is mentioned for example in Laid-Open Patent Publications Nos. 1-148265 and 1-148266.
In these prior art blood filters, as is stated for example in Laid-Open Patent Publication No. 1-148265, there is a housing, and in the blood filtering portion of the lower section of the housing, there is provided a filtering material made from a porous material that has been folded to form a plurality of pleats. This filtering material is rolled up within the housing so as to have a cylindrical shape with the pleats radiating outwardly therefrom. Then the open top end of the filtering material is sealed by forming a non-permeable portion obtained from the hardening of a potting material poured across such opening, and this is done in such a way that the interior surface of the non-permeable portion that faces towards the inside of the filtering material is formed as a flat, horizontal surface. Further, the blood outlet that is formed in the lower section of the housing communicates with the interior space of the filtering material.
When these blood filters are primed, the priming fluid enters from the blood outlet and fills up the interior space of the filtering material. At this time, by utilizing the pressure difference between the interior and exterior of the filtering material, any air bubbles existing in the priming fluid are discharged to the outside.